A Variable-Stiffness Joint Based on Electromagnetic Force Attraction: Modeling and Design

In this paper, we introduce the design and modeling of a novel variable stiffness joint based on electromagnetic force attraction. Thanks to this force, the stiffness can be modulated using the principles of friction force. The design comprises: a rotational joint, a commercial electromagnet, a support spring, and a rubber surface. This design is compact and presents low energy consumption, it is motivated by the need to control the stiffness of the rotational joints in robotics applications. The stiffness can be adjusted using an input voltage from zero to twelve volts. Energy efficiency is ensured through the application of a pulse width modulation module, which significantly reduces the electromagnet energy consumption and limits the heating for prolonged usage. The novelty of this research lies in the technique employed to modulate the stiffness using the magnetic field of an electromagnet and some rubber surfaces. Furthermore, the proposed physically-based model accurately aligns with the experimental results, particularly in terms of the continuous stiffness variation curves and the stiffness’s dependency on the rubber surface.